The present invention relates to a seabed-resource lifting device, and more particularly relates to a seabed-resource lifting device capable of causing rare-earth elements to rise from a seabed having a depth of 5000 meters or more.
Because the deep sea at a depth of 5000 meters or more is under high pressure of as much as about 500 atmospheres (500 kgf/cm2), i.e., 50 MPa, and the total weight of a riser pipe extending to the seabed becomes large, it is not possible to mine rare-earth elements in the deep sea on a commercial basis by using conventional techniques, which at most allow mud samples to be picked from the seabed by using a sampling device attached to the end of a wire.
Patent Document 1 discloses ore-lifting equipment that is capable of lifting ore from the seabed. This ore-lifting equipment includes (1) an ore-transport pipe through which seawater containing ore is transported to an offshore platform, (2) a circulation-transport pipe through which seawater is returned to the seabed from the offshore platform, (3) a circulation pump that sends seawater to the circulation-transport pipe, (4) a submersible pump that sucks in seawater containing ore from a suction port on the seabed and sends it to the ore-transport pipe, and (5) a water turbine that drives the submersible pump by using as a power source seawater flowing through the circulation transport pipe. Document 1 states that this ore-lifting equipment can be used at depths of 500 meters-2000 meters. However, ore-lifting equipment that can be used at a depth of 5000 meters or more has not been realized, because in order to collect mud-containing ore from the seabed at such a depth, the equipment requires both a long heavy pipe that is hung from an offshore platform and a strong pump that is capable of pumping seawater from the seabed up to a platform that is 5000 or more meters above.